Hot answers tagged

35

Even "dry" concrete contains considerable water, and is a relatively good conductor. So, it's a relatively good path to ground for a person touching it, increasing the odds of a lethal shock. Generally, for something to make it into the electrical code, some number of people have probably died due to the lack of it before that happened.


33

When or is it NEC code compliant to upgrade a 2-wire circuit, by adding a third prong equipment ground from a nearby galvanized cold water pipe? Never! Article 250.118 of the National Electrical Code lists the approved methods of equipment grounding. Water piping systems are NOT listed there. Metal piping systems within buildings are required to be bonded ...


29

Let me give some framework around what ThreePhaseEel said. I can understand wondering that, since UK appliances all have fuses in their plugs, and I bet the fuses are sized to protect the appliance. The US doesn't have those. It depends on reasonably close matching between receptacle and fuse/breaker protection. Thus, the general rule is that receptacles ...


27

The key lies in the way UL tests 15A and 20A receptacles Answering this question requires a deep dive into the standard UL tests 15A and 20A receptacle devices to, namely UL 498. In particular, we have to look at the way these receptacles are tested for acceptable loading, which is governed by Section 113 of the standard. We start with the fact that a 15A ...


23

The wires in NM aren't labeled for use outside the cable jacket, and may not be the correct type for use in conduit to begin with First off, the wires inside a NM cable are not marked or labeled at all, which automatically makes them unsuitable for use in a conduit wiring method, as NEC 310.120 requires conductor insulation to be marked/labeled with the ...


23

Adding the short wire is called pigtails and it is code compliant so yes you can do this. Pigtails are a superior way of making connections in my opinion. The pigtails do not add to the wire volume in the box.


22

The most important rule in NEC is 110.3(B), which requires you to follow labeling and instructions... which means read them. In this case, that only makes things better, particularly the boldface in 4a and 4b. These explain how to use Leviton's "back-wire" feature, which allows placing 2 wires under each screw. Pay heed to the word "FIRMLY&...


17

There is one safety issue here It appears that the original installer took the ground wire from the 12/3 cable, looped it around one switch ground screw, then attached it to the other switch ground screw. This grounds the switch yokes fine, but leaves the (metal) box ungrounded save through screw threads. The solution to this is to cut off the existing ...


17

The NEC doesn't count a receptacle above 5-1/2' to satisfy the requirement - 210.52(4) Located more than 1.7 m (51⁄2 ft) above the floor The NEC doesn't have a lower limit for height, in fact 210.52(A)(3) allows floor receptacles within 18" of the wall to satisfy the requirement. (3) Floor Receptacles. Receptacle outlets in floors shall not be ...


15

Those hangers will stick out and potentially catch on clothing. I would use saddles.


14

You don't need GFCI receptacles anywhere. Nobody cares how you provision the GFCI protection. You are welcome to have one GFCI device and feed all the receptacles from the protected zone (LOAD) of that GFCI device. You should take the time to learn exactly how downline protection works, and then, put LOAD to good use! That will greatly reduce the cost of ...


12

You can have a 14-60R in your house, but it must be on a dedicated branch circuit There is nothing in the NEC that prohibits you from having a 60A (or larger!) receptacle in your house. (While NEMA-style receptacles and plugs only go up to 60A, it is possible to get higher amp ratings in the form of industrial-style pin-and-sleeve connectors.) However, NEC ...


12

This is not allowed because it violates the rule that in any cable there must be two conductors carrying equal current in opposite directions so the magnetic fields cancel. That T- T Loop top right would have one traveler carrying current, no current in the other, and no neutral present carrying current in the opposite direction. The time varying magnetic ...


12

The clearance requirement is almost definitely going to be an issue. (And not an unusual issue - I will have the same problem if/when I ever upgrade my panel and get it inspected.) The shelves should be OK because you have room to the left. But the washer/dryer (whichever one is closer to the panel) is a definite problem. If there is any way to move it (but ...


12

My question is now that I'm running a 30 amp wire and only using 20 amps, do I need to run a neutral to send the unused 10 amps back the supply? There is no 'unused 10 A'. However (and this is physics, not building codes) if because you now have 30 A phase wires and you put 30 A breakers on them, and there is any possibility of you connecting an unbalanced ...


11

We're reading tea leaves here to guess at NFPA's intent. NFPA writes the "model electrical code" which they offer for anyone in the world to adopt as their law. But politically, NFPA has been having a big problem. Normally NEC changes are fairly trivial in cost: Pull a neutral wire on switch loops, gosh, you're using the /3 Romex instead of the /2. It'...


11

The Code doesn't specify location of protection. NEC 2017 210.8 Ground-Fault Circuit-Interrupter Protection for Personnel. Ground-fault circuit-interrupter protection for personnel shall be provided as required in 210.8(A) through (E). The ground-fault circuit interrupter shall be installed in a readily accessible location. Th 2020 Code changes (E) to (F), ...


10

Enclosure You start with an enclosure that includes a backplate (interior panel) -- usually this is purchased separately from the enclosure itself, but the manufacturers make sizes that fit mounting holes in their enclosure. Enclosures come in many sizes, different materials, different NEMA ratings, different cover options (screw-on/hinged, handles, ...


10

It's mandatory When putting identical-appearing circuits in a conduit, you must differentiate them somehow. It's mandatory. I would not bundle them but mark them individually. Black(blue) and White(blue) for instance being the obvious pair. Bonus points: use a decent length (2") of shrinkwrap so the tape doesn't come off someday. The reason I don't ...


10

Why 20A? Receptacle design constraints, most likely The reason why general receptacle circuits top out at 20A is because the notion of a duplex receptacle doesn't work for larger plug sizes (just can't fit enough meat in there at a suitable spacing for it to work), nor does the idea of a "shared" receptacle (T-slot) that can accept 15A or 20A plugs, as well ...


10

Derailed by Derating Your plan is a non-starter, even if you overcome the fill issues you're having, because of the other limit the NEC places on conduit fill; namely, the derating factors found in 310.15(B)(3)(a) that limit ampacity based on the number of current-carrying conductors. The first two rows of the table are normally not an issue because nobody ...


10

I see two options. What I see in the US quite a bit is instead of running the plastic channels on the wall surface, people will use steel conduit. It gives kind of a rustic/industrial look. Receptacles would then be mounted in steel boxes on the wall surface as well. What is typical in Germany, where most walls are block and plaster, is that grooves are cut ...


10

No philosophy: Code is data-driven Code is the result of analysis of systematically collected data about actual electrical accidents as they happened in the field. It’s the nature of science that you must take the field data as it comes, and not try to force it to conform to some notion of what it should be. In the case of 15/20A, the data has shown that ...


10

For EMT (anyway) the spacing is pretty clear - I can't recall if it's the same or different for other types, but it might well be the same. Within 12" of each box. 10 feet maximum spacing (1 clamp per stick of conduit, minimum.) You can do more than the minimums without an issue. You can't do less than that. So a typical 20 foot run would need at least ...


9

NEC 300.4(D) covers the type of installation indicated in the question, and it applies to both AC and MC armored cable. So you'll need to use a steel guard at least 1/16" thick to protect the cable. This tip from Fine Homebuilding illustrates this type of installation. Rather than backing the molding with steel plating, they use a U-shaped channel to ...


9

Nope. Nope nope nope. You cannot use 210.12(A)(4) to put AFCI at an outlet. There are certain fairly rare cases where you can put AFCI at the first outlet. However, there is a misconception that has turned into a regular "old wives' tale", that one can skip the expensive AFCI breaker and just slap an ACFI recep at the first outlet. Oh no you can't! ...


9

They are intended to be mounted outside the box... You are correct that they are intended to be mounted to a KO (usually on the breaker box), instead of being left inside, all flop-a-dop, as yours was. You can use this unit still, although you will probably want to leave some space around it, as its further lifespan is unknown. (All MOV-based suppressors ...


9

Or... just run the jacketed cable through the conduit It is permissible to run the entire, jacketed NM-B cable through the conduit. The restriction is that it takes a mighty bite out of conduit fill, because the NM-B cable must be treated the same as a round conductor of the wide dimension. This is particularly punishing when there are 2 "wires" (...


9

There is no "unused" 10 amps. You use the #10 wire because it's big enough to handle the 20 amps without overheating and in your case, without dropping the voltage. If you are running cable (flex, armored, whatever) you should run a /3 one with a neutral that you will not use but will be there in case needed in future. In case, for example, you ...


8

Be sure you use a 30A double-pole breaker to adequately protect your wiring. Make sure you provide an equipment ground and use a NEMA 14-30 receptacle. The box can be metal or plastic. Some form of cable clamp is always required, it's just that most plastic boxes have an integrated clamp (that finger-trap style door). If using NM cable, The cable must be ...


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